Assessment of cardio-respiratory fitness (CRF) is important in several fields, such as for the sports and fitness industry, for clinical diagnostic procedures, for prognostic and rehabilitation procedures, and for self-monitoring in asymptomatic individuals. The direct measurement of CRF requires maximal physiological effort, which is associated with a greater risk of cardiovascular events, and requires expensive devices and trained personnel. The indirect estimation of fitness overcomes some of these limitations but still requires the patient to undergo a rigorous specific protocol. Indirect estimation requires time and often involves the use of specific equipment (such as lab bicycles, steps, etc.).
Cardiovascular function is ascribable to maximal cardiac output, which, via Fick's principle, is related to maximal oxygen uptake (VO2max). In athletes, VO2max provides valuable information about their aerobic power. Aerobic power is a fundamental determinant of endurance sport performance and an indicator of training efficacy. In the clinical setting, VO2max provides key diagnostic and prognostic information in several clinical populations, such as patients with coronary artery disease or heart failure. Likewise, cardiovascular function assessment can be important to evaluate fitness in asymptomatic adults.
Although direct determination of VO2max is the most accurate method, it requires a maximal level of exertion by the subject. This results in a higher risk of adverse events in individuals with intermediate to high risk of cardiovascular problems. Moreover, a respiratory gas analysis system is needed, which requires operator expertise and involves additional costs.
Estimation of VO2max during sub-maximal exercise testing can offer an effective alternative. Over the past decades many protocols have been developed for this purpose. However, sub-maximal protocols require that the user follows a standardized exercise protocol. In many cases these exercise protocols require time (3 to 6 minutes) and small pieces of equipment (steps, treadmill, ergometers, etc.). Moreover, the exercise protocol has to be followed rigorously and usually requires the presence of trained personnel—such as a doctor, a researcher, or a personal trainer—in order to allow an accurate estimation of VO2max. Because of these requirements, VO2max cannot be calculated easily, anytime and everywhere.
Accordingly, there is a need for methods and apparatus to determine VO2max and other cardio-respiratory fitness parameters.